boy/girlcousin

Question

what if a girl has a cousin (boy) thats around the same age or older or even younger, and you two are together a lot bacause of family gatherings... whats the guidelines of that relationship? are you allowed to get a ride from him to somewhere? are you allowed to be friendly? can you give a wink if you saw him somewhere with other guys that you won't say something you'd rather wink...? these questions come up also when it's a close family friend that your like cousins or like brothers...? thanx so much for the clarification!